The present invention relates to digital data storage systems and methods, and more particularly to those providing fault-tolerant storage.
It is known in the prior art to provide redundant disk storage in a pattern according to any one of various RAID (Redundant Array of Independent Disks) protocols. Typically disk arrays using a RAID pattern are complex structures that require management by experienced information technologists. Moreover in many array designs using a RAID pattern, if the disk drives in the array are of non-uniform capacities, the design may be unable to use any capacity on the drive that exceeds the capacity of the smallest drive in the array.
One problem with a standard RAID system is that it is possible for disc-surface corruption to occur on an infrequently used area of the disk array. In the event that another drive fails, it is not always possible to determine that corruption has occurred. In such a case, the corrupted data may be propagated and preserved when the RAID array rebuilds the failed drive.
In many storage systems, a spare storage device will be maintained in a ready state so that it can be used in the event another storage device fails. Such a spare storage device is often referred to as a “hot spare.” The hot spare is not used to store data during normal operation of the storage system. When an active storage device fails, the failed storage device is logically replaced by the hot spare, and data is moved or otherwise recreated onto the hot spare. When the failed storage device is repaired or replaced, the data is typically moved or otherwise recreated onto the (re-)activated storage device, and the hot spare is brought offline so that it is ready to be used in the event of another failure. Maintenance of a hot spare disk is generally complex, and so is generally handled by a skilled administrator. A hot spare disk also represents an added expense.